(1) Field of the Invention
The present invention relates to a catalyst for generating hydrogen and a method for generating hydrogen.
(2) Description of the Related Art
Various methods are known for generating hydrogen gas to be supplied to fuel cells. Examples of such methods include the electrolysis of water; reactions between metals and acids; reactions of water with metal hydrides; the steam reforming of methyl alcohol or natural gas; and the release of hydrogen from hydrogen storage materials, such as hydrogen storage alloys, activated carbon, carbon nanotubes, and Li—N materials. However, these methods have drawbacks in which much energy is required to generate hydrogen, the amount of hydrogen generated is small relative to the amount of starting materials used, large-scale equipment is required, etc. For this reason, although these methods are applicable to hydrogen generation on an industrial scale or on a laboratory scale, they are not suitable for use in supplying hydrogen to fuel cells for automobiles, portable fuel cells for, for example, cellular phones and personal computers, and the like, which require a continuous supply of necessary amounts of hydrogen fuel, and for which there is a demand for miniaturization.
Metal hydrides, such as LiAlH4 and NaBH4, are used as hydrogen-generating reagents in laboratories and the like. These compounds need to be handled carefully because they rapidly release a large amount of hydrogen upon contact with water, producing an explosive phenomenon. For this reason, these compounds are also not suitable for use as hydrogen supply sources for the fuel cells mentioned above.
Methods for releasing hydrogen by utilizing hydrolysis reactions of tetrahydroborates, such as NaBH4 (see, e.g., Patent Literature 1 and 2, and Non-Patent Literature 1 and 2 listed below), and hydrolysis reactions of ammonia borane represented by the chemical formula NH3BH3 (see, e.g., Patent Literature 3, and Non-Patent Literature 3 and 4), have also been reported. However, these methods have problems related to the recovery and regeneration of the resulting borate compounds.
Hydrazine (H2NNH2), which is liquid at room temperature and has a high hydrogen content (12.5% by weight), is considered to be promising as a source of hydrogen. Hydrazine is reported to be capable of being decomposed into nitrogen and hydrogen by catalytic reactions. For example, Patent Literature 4 listed below discloses a method for generating hydrogen that comprises contacting hydrazine or a derivative thereof with a metal capable of catalyzing the generation of hydrogen, such as nickel, cobalt, iron, copper, palladium, or platinum. However, an investigation of the ability of these metal catalysts to catalyze the generation of hydrogen via decomposition reactions of hydrazine revealed that a sufficient amount of hydrogen is not produced using these catalysts (see Non-Patent Literature 5 below).
Further, Patent Literature 5 discloses a system for producing hydrogen, comprising a decomposer that decomposes ammonia or hydrazine, which is used as a hydrogen source, into nitrogen and hydrogen, and supplies them into fuel cells. However, Patent Literature 5 does not disclose the details of a method for generating hydrogen by the decomposition of hydrazine.
Patent Literature 6 and 7 disclose methods for generating hydrogen by contacting an aqueous hydrazine solution with a catalyst comprising rhodium supported on a support containing alumina or silica. However, according to these methods, hydrogen is not produced from hydrazine at a high yield, resulting in an insufficient amount of hydrogen.